At present, you must provide the client-side ID of the element from which you want to remove the loading panel, which you cannot have when the loading panel is a DefaultLoadingPanel, for example, or when there has been an error and you simply want to hide all loading panels so the end user can continue working with the page. Calling hide() without arguments should hide all instances of the loading panel, regardless of the elements over which they are shown.
The RadAjaxManager and RadAjaxPanel are having such method called hideLoadingPanels();